1. Field of the Invention
This invention relates to MEMS oscillators and more particularly to power handling associated therewith.
2. Description of the Related Art
Microelectromechanical Systems (MEMS) generally refers to an apparatus incorporating some mechanical structure having dimensions, less than, e.g., approximately 100 or 200 μm. MEMS devices are commonly used for such applications as oscillators in timing applications, accelerometers, and inertial sensors, and the number of applications is growing. Certain structural components of a MEMS device are typically capable of some form of mechanical motion. The MEMS device can be formed using fabrication techniques similar to techniques used in the electronics industry such as Low Pressure Chemical Vapor Deposition, (LPCVD), Plasma Enhanced CVD (PECVD), patterning using photolithography, and Reactive Ion Etching (RIE), etc.
MEMS devices used in timing applications include a resonator. The resonator may have a variety of physical shapes, e.g., beams and plates. FIG. 1 illustrates a conventional resonating MEMS device 100 that has a resonating member 101 coupled to an anchor 102, which in turn is coupled to the substrate 103. The MEMS device includes electrodes 105 and 107 forming electrostatic transducers with the resonating member. One of the electrodes functions as a drive electrode and the other, a sense electrode. The electrodes are coupled to appropriate voltage levels provided through appropriate conductive paths in the substrate and the resonating member 101 is coupled to an appropriate voltage level through the anchor 102. During operation, a drive electrode 105 electrostatically drives resonator 101, using a voltage differential that exists between the drive electrode 105 and resonator 101, so that resonator 101 dynamically deflects as illustrated by arrow 109 in a plane parallel to the substrate 103. A sense electrode 107 detects a change in capacitance as the capacitance varies between resonator 101 and sense electrode 107 due to the “in-plane” motion of resonator 101. The voltage sensed due to the change in capacitance corresponds to the resonating frequency of the beam 101. An oscillator circuit (not shown) typically uses the output from the sense electrode and maintains the MEMS device at a resonant frequency using the drive electrode. As is well known in the art, other vibration modes such as out-of-plane or torsional modes exist for MEMS devices.
As MEMS oscillators have the advantage of small form factor and low-cost production, they can be found in a variety of consumer products, including portable products using batteries to supply power. Improvement in power handling in MEMS oscillators is desirable to provide better performance.